1. Field of the Invention
The present invention relates to a lens transfer device and a camera module having the same.
2. Description of the Related Art
Recently, portable terminals such as mobile phones and personal digital assistants (PDA) having a camera embedded therein are launched, and consumers also request terminals having a camera embedded therein, the camera having a variety of functions. Such a camera embedded in mobile terminals is constructed by attaching a lens to an imaging element such as charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) image sensors, and photographs an object and stores the image data of the object in a predetermined recording medium.
With the recent development of mobile terminals such as portable phones and PDAs, the mobile terminals provide a phone call function and are used as multi-convergence devices. The most representative of the multi-convergence devices is a camera module. The resolution of the camera module changes from 300,000 pixels (VGA) to 7,000,000 pixels. Moreover, the camera module provides various additional functions, such as auto-focusing (AF) and optical zoom.
In particular, demand for mobile terminals having a camera module with an autofocusing (AF) function is rapidly increasing, because a high-quality image in which focusing is achieved can be provided, regardless of a focal distance from an object. However, as a variety of functions including the AF function are implemented, the number of components embedded in the camera module increases. Therefore, the entire size of the camera module inevitably increases, compared with the size of a general camera module.
Therefore, when the camera module is mounted on a mobile terminal, there are difficulties in performing an assembling process because of lack of a mounting space for the camera module.
Further, since an automatic or manual driving method is applied depending on a driving method and a camera embedded in a mobile phone should be manufactured with a small size, a macro function for photographing a close object at an accurate focus is implemented by focus adjustment using a minute position change of a lens.
Since the macro function by the manual driving method can be implemented by a relatively cheap and simple structure in comparison with the automatic driving method, the manual driving method is mainly applied to a camera for mobile phones. The focus adjustment of the lens is performed by a structure which directly drives the lens through a lever projecting outward from the lens.
Conventionally, to perform the AF function and the macro function, a cam driving method has been mainly used. In the cam driving method, as the relative distance between lenses is changed along a cam-shaped groove positioned on a side surface of a lens barrel which is driven by an electromagnetic motor, the respective lenses are vertically driven.
FIG. 1 is a diagram showing the structure of a conventional lens driving device disclosed in U.S. Pat. No. 6,268,970. The conventional lens driving device includes frames supporting lens groups 120, 130, and 140 and cam tubes 160 and 170 supporting the frames. The respective cam tubes support the frames such that the frames can relatively move in the direction of the optical axis of an optical system, and are driven by an actuator 110.
In such a lens driving device, the relative positions of the respective lenses are determined by the shape of a cam. Therefore, a focus lens and a focus adjusting mechanism for adjusting a focus at a specific magnification are additionally required, and a driving mechanism such as a lens holding mechanism, which moves along a final reduction gear and the cam, becomes complex.
FIG. 2 is a diagram showing another conventional lens driving device disclosed in Korean Patent Laid-open Publication No. 2000-55180. The conventional lens driving device includes a fixed lens group 201 coupled to a camera body 200, the fixed lens group 201 including a plurality of lenses. The camera body 200 has a housing space formed therein, and a zoom motor 203 is housed in the housing space. The zoom motor 203 has a shaft coupled to a guide screw 205, and the guide screw 205 has a screw thread and a screw groove formed on the outer circumference thereof. Further, a clip 207 for transmitting power is coupled to the outer circumference of the guide screw 205. The clip 207 has a screw thread and a screw groove formed thereon. The screw thread and the screw groove of the clip 207 have the same shape as the screw thread and the screw groove of the guide screw 205 such that one side of the clip 207 contacted with the guide screw 205 is coupled to the screw thread and the screw groove of the guide screw 205. One side of the clip 207 is coupled to a zoom barrel 209. The zoom barrel 209 is coupled to a moving lens group 202. The zoom lens barrel 209 is coupled to a guide shaft 211 disposed in an optical-axis direction so as to move along the guide shaft in the optical-axis direction.
In the zoom lens mechanism constructed in such a manner, when the zoom motor 203 rotates, the guide screw 205 is rotated. Then, the torque of the guide screw 205 is converted into a straight-line motion by the clip 207. Therefore, the clip 207 moves straight in the optical-axis direction. As the clip 207 moves straight, the zoom barrel 209 moves along the optical-axis direction. When the zoom barrel 209 moves along the optical-axis direction, a portion of the zoom barrel 209 coming in contact with the guide shaft 211 is slid in such a manner that the zoom barrel 209 can reciprocate in the optical-axis direction.
In the zoom lens mechanism constructed in such a manner, since an electromagnetic motor is used, electromagnetic waves may occur. Therefore, the application of the zoom lens mechanism into small-sized communication devices is limited. Further, since the electromagnetic motor is used, a final reduction gear is used, so that the mechanical structure of the zoom lens mechanism becomes complex. Further, in order to adjust a focus, the zoom lens and the focus lens should be moved independently from each other.
Recently, an ultra-small optical zoom lens mechanism has been developed so as to be applied to a small optical system having a zoom function. In such an ultra-small optical zoom lens mechanism, an electromagnetic motor is not used, but an intellectual element such as a piezoelectric element is mainly used. As the electromagnetic motor is substituted with the piezoelectric element, a driving mechanism for driving a lens can be simplified, which makes it possible to achieve high efficiency.
FIGS. 3 and 4 are diagrams showing a further conventional lens driving device using such a piezoelectric element, disclosed in U.S. Pat. No. 6,215,605. In the conventional lens driving device, piezoelectric actuators 311a and 311b are fixed to base blocks 321 and 322, respectively, and their expansion and contraction are transmitted to driving rods 316 and 317. Then, lenses L2 and L4 are transferred by pre-pressure generated from sliding portions 331a and 332a and an inertia force of lens holders 331 and 332. As the lens holders are transferred or slide with the driving rods in accordance with the waveform of the pressure of the piezoelectric actuators 311a and 311b, the lenses L2 and L4 can be transferred in both directions.
When the displacement of one piezoelectric actuator between adjacent piezoelectric actuators 311a and 311b is transmitted through the base block 313, the displacement may be transmitted to another lens. Therefore, the base block 313 has a groove 313g formed therein so as to prevent the transmission of displacement between the piezoelectric actuators. As the groove is formed, the structure of the lens driving device becomes complex. Further, the displacement interference between the piezoelectric actuators cannot be perfectly removed.
Further, the length of the driving rods 316 and 317, which are moved by the piezoelectric actuators so as to transfer the lenses, is limited depending on the size of the piezoelectric actuators. The limitation of the length of the driving rods causes the limitation of lens transfer distance, thereby having an effect upon product performance.
In this case, since the driving rods are fixed, the length of a barrel having lenses built therein cannot be changed. In addition to a space for the transfer distance of the lenses, a separate space in which other components are arranged is necessary, which makes it difficult to reduce the size of the device. Further, since only one ends of the lenses are supported by the driving rods, asymmetrical displacement occurs in the lenses such that the lenses are likely to be unstably driven.